1. Field of the Invention
The invention relates to a method of forming silicide in semiconductor devices and, more particularly, to a method of forming a silicide layer in contact with a silicon substrate.
2. Description of the Background Art
In the manufacture of integrated circuits, intermediate or transition layers are often used as a metal barrier layer to inhibit the diffusion of metals into an underlying region beneath the barrier layer and/or to enhance adhesion of subsequently formed layers. These underlying regions include transistor gates, capacitor dielectric, semiconductor substrates, metal lines, and many other structures that appear in integrated circuits.
For example, when an electrode is formed from a transistor""s gate, a diffusion barrier is often used between the gate material and a metal layer that contacts the gate electrode. The diffusion barrier inhibits metal diffusion into the gate material, which may be composed of polysilicon. Such metal diffusion is undesirable because it would change the characteristics of the transistor, or render it inoperative. A combination of titanium/titanium nitride (Ti/TiN), for example, is often used as an adhesion/diffusion barrier.
Such a barrier stack is also used in a tungsten (W) metallization process to provide contacts to source and drain regions of the transistor. The barrier stack prevents undesirable metal diffusion between the tungsten plug and the underlying silicon (Si) substrate. For example, a Ti layer is typically deposited upon the contact regions of a Si substrate, followed by conversion of the Ti layer into an intermediate titanium silicide (TiSi,) layer, which provides a lower resistance contact with Si. If the Ti deposition is performed using plasma enhanced chemical vapor deposition (PECVD), e.g., at a temperature between 550-700xc2x0 C., a reaction will occur between the Ti film and the underlying silicon substrate at the bottom of the contact. This leads to the formation of a titanium silicide (TiSix) layer upon the silicon substrate. Alternatively, if the Ti film is deposited using physical vapor deposition (PVD), then the TiSix layer at the bottom of the contact may be formed in a separate rapid thermal process (RTP) step, either prior to or during subsequent film processing. A TiN layer is then formed upon the TiSix layer, followed by the formation of a tungsten (W) plug. In addition to being a barrier layer, the TiN layer serves two functions: 1) prevents chemical attack of TiSix by tungsten hexafluoride (WF6) during W deposition; and 2) acts as a glue layer to promote adhesion of the W plug.
Presently, integrated circuit devices have feature sizes in the range of about 0.25 micron (xcexcm). As future generations of semiconductor devices approach the sub-0.25 xcexcm and sub-0.18 xcexcm regimes, devices will have relatively shallower junctions or trenches on the same substrate. Typically, formation of the intermediate TiSi, layer requires sacrificing a portion of the Si substrate as a Si source. With decreasing thickness of available Si, such Si consumption will lead to deterioration of the electrical characteristics of the substrate and devices formed thereon will result in a failed or substandard end product.
Therefore, a need exists in the art for an alternate method of forming silicide layers without compromising substrate quality or device characteristics.
The invention provides a method for forming a silicide layer in contact with a silicon substrate. The method comprises forming a metal-containing layer upon a Si substrate, exposing the metal-containing layer to a silicon-containing source that is different from the silicon substrate. The metal-containing layer reacts with the silicon-containing source and results in the formation of a metal silicide layer having silicon originating primarily from the silicon-containing source.